The present invention relates to a projection type liquid crystal display apparatus using polarizing beam splitters and, more specifically, to a projection type liquid crystal display apparatus that can improve the efficiency of light utilization, reduce the apparatus size, and provide a uniform brightness distribution of a projection screen.
In recent years, with the increased need of displaying images on a large screen, projection type liquid crystal display apparatuses have come to be used, which project, with magnification, a display content of a small-size liquid crystal display device onto a screen or the like.
FIG. 7 shows a configuration of a projection type liquid crystal display apparatus of a first conventional example. A high-intensity white light source 10 is a metal halide lamp, for instance. A parabolic reflecting mirror 11 reflects part of a light beam emitted from the light source 10, to produce a parallel light beam. A heat wave filter 100 absorbs or reflects heat waves of the light beam coming from the reflecting mirror 11. A polarizer 31 converts a heat-wave-eliminated parallel beam to linearly polarized light. A liquid crystal display device 40 modulates the linearly polarized light in accordance with an image signal. An analyzer 32 transmits only part of the linearly polarized light whose polarization direction is along its transmission axis. A projection lens 50 projects, with magnification, transmitted linearly polarized light onto a screen 60.
However, in the projection type liquid crystal display apparatus having the above configuration, of the light beam emitted from the light source 10, only the linearly polarized light that is transmitted by the polarizer 31 is used as illumination light for the liquid crystal display device 40, and the other linearly polarized light whose polarization direction is perpendicular to the linearly polarized light transmitted by the polarizer 31 is lost. That is, only about 40% of the light beam emitted from the light source 10 is used as the projection light. Therefore, the above projection-type liquid crystal display apparatus is low in the efficiency of light utilization and its projection screen is dark.
To solve the above problems, U.S. Pat. No. 5,283,600 (Japanese Patent Application No. Hei. 4-33821 filed Feb. 21, 1992) proposes a projection type liquid crystal display apparatus in which the polarization direction of linearly polarized light emitted from a light source is so converted as to become parallel with that of P- or S-polarization light, and which therefore can effectively utilize the light emitted from the light source as illumination light for a liquid crystal display device.
Referring to FIG. 8, the projection type liquid, crystal display apparatus disclosed in above-mentioned application Hei. 4-33821 will be described as a second conventional example.
As shown in FIG. 8, a polarizing optical system 120 is composed of a polarizing beam splitters 121 and 122, light beam reflecting elements 123 and 124 and phase plates 125 and 126.
Linearly polarized light emitted from a light source 10 is made incident on the polarizing beam splitters 121 and 122, and separated into P- and S-polarization components by polarization separating surfaces 121a and 122a. That is, the polarizing beam splitters 121 and 122 transmit one of the P- and S-polarization components to the side of a liquid crystal display device 40 while reflecting the other component by the polarization separating surfaces 121a and 122a.
Mounted so as to be inclined, by about 45.degree., from the reflection light exit faces of the respective polarizing beam splitters 121 and 122, the light beam reflecting elements 123 and 124 reflects the reflection light beams coming from the polarization separating surfaces 121a and 122a toward the liquid crystal display device 40.
Disposed in optical paths of the respective reflection light beams reflected by the light reflecting elements 123 and 124, the phase plates 125 and 126 transmit the reflection light beams while performing phase conversion on those light beams. The phase plates 125 and 126 converts the polarization direction of the reflection light beams into a direction that is parallel with that of the transmission light beams from the polarizing beam splitters 121 and 122.
Other projection type liquid crystal display apparatuses using a polarizing beam splitter are disclosed, for instance, in Japanese Unexamined Patent Publication No. Hei. 3-152523 (published Jun. 28, 1991) and Japanese Unexamined Utility Model Publication Nos. Hei. 2-29076 (published Feb. 23, 1990) and Hei. 2-121779 (published Oct. 3, 1990).
However, in the projection-type liquid crystal display apparatus of U.S. Pat. No. 5,283,600, the light beam emitted from the light source 10 is separated into two parts going rightward and leftward by the two polarizing beam splitters 121 and 122. The polarizing beam splitters 121 and 122 occupy a large space in the optical axis direction, causing a problem that the apparatus is large and heavy. In addition, the large polarizing beam splitters 121 and 122 make the apparatus expensive.
Further, in the above projection type liquid crystal display apparatus, since the illumination light beams enter the liquid crystal display device 40 at its three portions, i.e., a central portion and both side portions, three peaks appear in the illuminance distribution of the illumination light (see FIG. 9), which makes the brightness distribution of a projection screen non-uniform; that is, deteriorates its image quality.
Japanese Unexamined Patent Publication No. Sho. 63-182987 (published Jul. 28, 1988) proposes a projection type liquid crystal display apparatus in which light emitted from a light source is caused to enter one side end portion of a plurality of polarizing beam splitters aligned along the optical axis, and a light beam is output in one direction from one side face of the plurality of polarizing beam splitters.
However, the apparatus having the above configuration is large in the optical axis direction. Further, since the light beam emitted from the light source is inputted to the single polarizing beam splitter, the light incident surface is small. This causes a problem that part of the light beam emitted from the light source does not enter the polarizing beam splitter, i.e., is not utilized. Therefore, the efficiency of light utilization is low.